Four months after French troops cleared Islamist fighters from the desert towns of northern Mali, U.S., French and African governments see a worrying new trend: Many of the same militants are regrouping in neighboring countries.

One new trouble spot, say officials from the U.S., France and Niger, is an expanse in southwest Libya that is roughly 1,000 miles from Mali, beyond the reach of French warplanes and in area that before now drew little U.S. notice.

The militants' recent movements pose a growing danger to weak African states. Militants have launched a series of deadly terrorist attacks this past week, including one in a town in Niger where the U.S. plans to put a new drone base. The developments also spotlight the difficulty of combating al Qaeda in areas where governments don't have the forces to control their vast borders.

ENLARGE

The wreckage of a suicide bomber's vehicle at an army base in Niger on Thursday, in a Niger TV video grab.
Agence France-Presse/Getty Images

But the West's ability and willingness to respond is less clear-cut than ever. In a major policy speech Thursday, President
Barack Obama
raised the bar for U.S. lethal action against terrorist groups, saying the U.S. will strike only at those who pose an imminent threat to Americans, rather than at terrorists who threaten U.S. allies and interests.

"Some U.S. government officials clearly want to end the war on terrorism. But there is a big discrepancy between hope and evidence," said
Seth Jones,
an al Qaeda specialist with the Rand Corp. who advised the military in Afghanistan. "Al Qaeda and its affiliated groups have increased their presence in North Africa and the broader Middle East. Like it or not, terrorists get a vote too."

A top concern is Niger. At dawn Friday, French special forces there exchanged gunfire with several fundamentalists strapped with explosive belts, eventually killing them. The militants had taken over an army barracks in the remote trading town of Agadez, according to officials in France and Niger.

The clash followed twin suicide blasts Thursday that struck the same Agadez barracks as well as at a uranium mine 100 miles to the north operated by French nuclear engineering company
Areva
SA
. The attacks left at least 19 soldiers and one civilian dead, Niger's government said.

Mokhtar Belmokhtar
—the Algerian-born militant who claimed responsibility for a January attack against an Algerian gas plant that left at least 38 employees dead, including three Americans—also claimed responsibility for Thursday's attacks.

French Defense Minister
Jean-Yves Le Drian
said the French campaign in Mali, which it launched in January after Islamist militants took over much of the country's north, succeeded in preventing terrorists from controlling that area.

"Now, we must avoid similar risks from materializing in northern Niger and parts of Chad," he said Friday, after the latest attacks.

The militants' movements highlight what one senior European defense official called a "wake-up call" for the West: While Mali has stabilized, French and U.S. intelligence reports now show militants from Mali have been able to cross the region's porous borders and establish a tentative new base in southwest Libya.

"It's a concern that squeezing a balloon on one end will create a pocket of terrorists on the other," a senior U.S. official said of al Qaeda and its allies in that part of Africa.

The U.S. believes that the southwest corner of Libya is now attracting Islamist fighters from Ansar al Dine and al Qaeda in the Islamic Maghreb who fled from Mali. In Libya, these groups are blending with local militant groups, including members of Ansar al Sharia, which the U.S. implicated in the 2012 attacks on U.S. outposts in Benghazi, in eastern Libya.

A former U.S. official said militants have set up rudimentary training camps in southwest Libya from which they could plan further attacks in the region.

The senior U.S. official said it was premature to call this a new safe haven area. "It's more like a refuge area for extremists who don't want to be hit in Mali," the official said.

Libya's postrevolution government is in disarray and Western officials say it is unclear who, if anyone, is responsible for security. While Libyan forces have some presence in the country's main population centers, large desert areas are controlled by a patchwork of tribes. "You are talking about a zone where there is no real authority," a senior European defense official said.

Libyan officials say they have given French and U.S. forces permission to increase surveillance of the area. But French and U.S. officials said they haven't gotten the green light for all of the missions they seek.

In a recent series of meetings in Washington and London, French officials told their American and British counterparts that the threat "zone is evolving" as Mali militants have increasingly moved out of reach.

The spread of al Qaeda affiliates across largely ungovernable reaches of the Sahara—and their growing strength in the Syria conflict—highlights a possible mismatch between a threat whose boundaries are expanding and a U.S. administration that is narrowing its counterterrorism role, current and former U.S. and European officials say.

The Pentagon has expanded its presence in Africa and recently started flying unarmed drones out of Niger. But Pentagon officials say their plate is full with the war in Afghanistan and with permanent military deployments in the Middle East and Asia to counter threats from Iran and North Korea. Added to that is Syria's civil war, which threatens to engulf the Middle East in a regional conflict.

Pentagon officials say they don't have enough drones to meet existing commitments, let alone cover the Sahara, a region about the size of Europe but with only 4 million inhabitants. Counterterrorism campaigns in Iraq, Afghanistan, Pakistan and Yemen have shown how dense networks of drones and spies can be used to dismantle terrorist networks, but that isn't likely for the U.S. in Africa anytime soon.

In the last four months of fighting in Mali, the French government says its warplanes and commandos have killed an estimated 800 militants linked to al Qaeda and its allies, helping the West African country to recover control over its territory and setting the stage for free elections.

But many insurgents previously based in northern Mali have eluded the French-led military intervention by resettling elsewhere, French government officials say. One of the most elusive has been Mr. Belmokhtar.

In a statement to the Mauritanian newswire Agence Nouakchott d'Information, the one-eyed Islamist leader allegedly said Thursday's attacks were conducted by militants from across the Sahara.

In March, the government of Chad said its soldiers had shot dead Mr. Belmokhtar. French officials have said they had no evidence Mr. Belmokhtar was killed and said they were taking his alleged statement to ANI "seriously."

U.S. intelligence agencies believe Mr. Belmokhtar is alive but his location is unknown. Current and former officials said he was last traced to northern Mali but it is unclear if he has relocated to southwest Libya with the other fighters.

In December 2012, the Libyan Congress declared the southwest desert border region a closed military zone. The chief of staff, Yousef Mangoush, organized a more professional border guard unit to patrol there as well as a separate unit to guard critical infrastructure facilities like oil fields and barracks where foreign oil company employees work and live.

However, Libya's armed forces don't have the high-tech aerial equipment necessary to survey the miles of empty desert.

U.S. and French officials say that their efforts to monitor the Libyan desert have been slowed by the Libyan government's resistance to allowing outside access to the area.

European Union officials said the bloc was trying to speed up the start of a two-year training mission aimed at helping Libya control its borders.

Libyans have held several security meetings in recent months with their neighbors to discuss border problems, but they have been struggling domestically, in the wake of Moammar Gadhafi's overthrow, to reform and professionalize all of their security forces.

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